CI uses basic concepts of quantum mechanics to provide substantial improvements to throughput and performance compared to conventional technologies, which are based solely on classical physics.
U.S. Pat. No. 5,955,992 provides the first disclosure of CI. PCT/US00/18113 describes applications of CI to coherence multiplexing and spatial interferometry. PCT Appl. PCT/US99/02838 describes applications of CI to direct-sequence code division multiple access (DS-CDMA). Applications of CI to DS-CDMA are also described in “High performance broadband DS-CDMA via carrier interferometry chip shaping” (C. R. Nassar and Z. Wu, 2000 International Symposium on Advanced Radio Technologies, Boulder, Colo., Sep. 6-8, 2000) and “MMSE frequency combining for CI/DS-CDMA” (Z. Wu and C. R. Nassar, IEEE Radio and Wireless Conference, Denver, Colo., Sep. 10-13, 2000).
The application of CI to multi-carrier code division multiple access (MC-CDMA) is described in “Introduction of carrier interference to spread spectrum multiple access” (C. R Nassar, B. Natarajan, and S. Shattil, IEEE Emerging Technologies Symposium, Dallas, Tex., 12-13 Apr. 1999). Applications of CI to time division multiple access (TDMA) are described in “Exploiting frequency diversity in TDMA through carrier interferometry” (B. Natarajan, C. R. Nassar, and S. Shattil, Wireless 2000: The 12th Annual International Conference on Wireless Communications, Calgary, Alberta, Canada, Jul. 10-12, 2000).
CI may also be applied to orthogonal frequency division multiplexing (OFDM). N-point transforms used in OFDM, such as fast Fourier transforms (FFTs) and inverse FFTs (IFFTs), essentially map one set of data symbols onto another set of data symbols. Each transform of a transform pair provides the basis for mixing symbols together to form a code that can be reversed by the complementary transform. Various techniques have been developed to efficiently process Fourier transform algorithms, such as described in U.S. Pat. Nos. 6,169,723, 6,137,839, 5,987,005, 5,297,236, and 5,365,470.
One technique for implementing a Fourier-transform type of coding includes filtering a time-domain sequence of input symbols. A polyphase FIR filter bank can be implemented equivalently with an N-point DFT or inverse DFT (as illustrated by J. G. Proakis in “Digital Signal Processing,” 3rd edition, p 825-831). Linear FIR filtering performed via the DFT typically involves segmenting the input symbols into blocks. The blocks are processed via the DFT and/or the IDFT to produce a block of output data. Common filter techniques include the overlap-save method and the overlap-add method. The resulting output symbols are complex-weighted sums of the input symbols.
None of the prior-art references implement direct-sequence coding based on CI polyphase codes. None of the prior-art references exploit phase relationships between orthogonal CI carriers to simplify transform operations or approximations of transforms.